FOSSIL LAND MAMMALS AND WESTERN NEARCTIC FAUNA 



121 



ORIGIN AND DISPERSAL OF LIVING 

 NEARCTIC MAMMALIAN FAMILIES' 



REGION S 



I 1 



PALEARCTIC NEARCTIC 



Didelphidae E -• L 



Soricidae L -• ? L 



Talpidae L ^L 



Scalopodinae L -• ? L 



Phyllostomatidae^ L -* ?— 



Vespertilionidae^ \J "^ ^ L 



Molossidae^ L' ? L 



Hominidae L' ^ L 



Dasypodidae^ L -* 



Ochotonidae L ? *- L 



Leporidae L *- L 



Aplodontidae E -■ L 



Sciuridae L -• ? L 



Geomyidae^ L 



Heteromyidae^ L 



Castor idae L •" L 



Cricetidae L "?" L 



Microtinae L -• ? L 



Muridoe^ L ■ L 



Zapodidae L ^ L 



Zapodinae L -< ? L 



Erethizonfidae^ L -• 



Canidae L ^?— L 



Ursidae L ^ L 



Procyonidae L ^?-" L 



Mustelidae L ? ^ L 



Felidae L ?- ^L 



Toyassuidae E ^?-* L 



Cervidae L ? ^L 



Bovidae L *- L 



Antilocapridae L 



E-extinct 

 L-living 



'-Based on Simpson(l947). 

 2-Not discussed by Simpson(l947). 

 '-Might have originated in the Paleotropic Region. 



Fig. 8. 



NEOTROPIC 





— L 



— L 



-^L 



-►L 



— L 

 -*-L 

 ■*■ L 



— L 

 -^L 



— L 



— L 



— L 



A consideration of the time of origin of the 28 Hving Nearctic 

 famihes (Fig. 9), supports the generaHzation that the Oligocene or 

 possibly late Eocene-Oligocene, was the interval of inception of 

 modern families of mammals.'^ 



The living genera of Nearctica are either autochthonous or have 

 immigrated from Palearctica or from the Neotropics. Interpretation 



2 Old World and South American families have a comparable geochronologic history. 



